High-Precision Regulation of a Pressure Controlled Artificial Mouth: The Case of Recorder-Like Musical Instruments

Real-time regulation of air pressure in an artificial mouth is studied. A closed-loop strategy is developped, including a controller algorithm which updates (according to the difference between the target and the measured blowing pressure) the electrical command sent to the servo-valve providing air flow. In this paper the targets considered may be steady states or slowly varying trajectories. Since both the musical instrument and the servo-valve behave nonlinearly, the design of the controller algorithm requires preliminary modelling and identification steps in order to optimize the compromise performances/robustness. The controller finally adopted for the experiments is a PI (Proportional Integral) which integral gain is adapted according to an online estimator. Moreover, a carefully tuned dither signal is added on the electric command in order to limit consequences of friction inside the servo-valve. The high-precision regulation is used to investigate the behaviour of the recorder. Firstly, it allows to highlight the existence of aeolian sounds which have never been observed on a recorder. Moreover, the influence of some small "details" of the chamfer geometry on the global behavior of the instrument is investigated. Hence the influence of the instrument maker's work can be evaluated, as well as the important consequences on the possibilities offered to the player: with the optimized chamfers, the instrument can sound louder and the transition between the two regimes is safer (larger hysteresis width).